The present invention relates to liquid crystal displays. More particularly, the invention relates to a technique for resolving major defects in a normally white liquid crystal display.
Liquid crystal displays (LCDs) are used in a variety of different applications. For example, LCDs are used in laptop computers, hand-held devices, cellular phones, coordinate location systems and vehicle displays. One type of an LCD is a normally white LCD. Pixels in normally white LCDs will be non-transmissive when power is applied to the pixel when driven black. Pixels that remain transmissive when power is applied are defective and known as xe2x80x9celectrically openxe2x80x9d or xe2x80x9cbright onxe2x80x9d pixel defects. When these defects occur in quantity, there is reason for a quality rejection of the LCD.
Most users of LCDs will permit some quantity of defects. However, a xe2x80x9cbright onxe2x80x9d defect is considered a xe2x80x9cmajorxe2x80x9d type defect (compared to an electrically shorted pixel or partially shorted pixel, which are considered minor defects). Technology currently exists to reduce the adverse impact of a bright on pixel in a xe2x80x9cnormally blackxe2x80x9d LCD (caused by an electrical short) and, depending on the thin film transistor (TFT) structure, in some normally white LCDs. Using this technology, when electrical shorts are detected in a normally black LCD, a laser is used to isolate the circuit from the bus line on the TFT substrate. This technology, however, will not work for all normally white LCDs, and in particular will not work for normally white LCDs in which the bright on defect is caused by an open circuit. Thus, improvements are necessary to develop techniques to resolve xe2x80x9cbright onxe2x80x9d pixel defects in a normally white LCD.
A technique is provided to resolve xe2x80x9cbright onxe2x80x9d pixels defects in a normally white LCD. A laser operating with a 780-840 nm wavelength in the visible range permits the ablation of the pigmented color filter material coated or adhered to a glass substrate of the LCD without causing thermal or mechanical damage to the glass substrate. The laser is used to darken the defective pixel by focusing on a color filter of the defective pixel. After a portion of the color filter is darkened, a minor defect exists instead of a major defect.